Multimode radio frequency structure exhibiting hybrid operation



Dec. 7, 1965 w. c. CUMMINGS 3,222,620

MULTIMODE RADIO FREQUENCY STRUCTURE EXHIBITING HYBRID OPERATION Filed May 21, 1962 3 Sheets-Sheet 1 [/1 I INYENTOR Wollmm C Cizmmzzzya vx 6 a W ATTORNEYS 7, 1965 w. c. CUMMINGS MULTIMODE RADIO FREQUENCY STRUCTURE EXHIBITING HYBRID OPERATION Filed May 21, 1962 3 Sheets-Sheet 2 INVENTOR W'Zlz'am L. Uammz'njs ATTORNEYS Dec. 7, 1965 w. c. CUMMINGS MULTIMODE RADIO FREQUENCY STRUCTURE EXHIBITING HYBRID OPERATION 3 Sheets-Sheet 5 Filed May 21, 1962 BY William C Cmzmz'zzgfl ATTORNEYS United States Patent 3,222,620 MULTIMUDE RADH) FREQUENCY STRUCTURE EXHIBHTING HYBRID OPERATION William C. Cummings, Alexandria, Va, assignor to Scanwell Laboratories, Inc, Springfield, Va., a corporation of Virginia Filed May 21, 1962, Ser. No. 196,421 8 Claims. (Cl. 33311) This invention relates to radio frequency networks and, more particularly, to transmission line networks, which have properties in some respects similar to those of impedance bridges or hybrids.

One object of the present invention is a transmission line network having several inputs and a number of outputs, interconnected in such a manner that when the outputs are terminated with equal impedances, the inputs become substantially independent of one another so that power delivered to any one of the inputs proceeds to the impedances connected to the outputs rather than to any of the other inputs.

Another object of the present invention is to provide an antenna having a single structure which can be energized from several independent terminals such that the antenna structure radiates with different characteristics for the different terminals.

Additional objects will become apparent as the description proceeds with reference to the drawings, wherein;

FIG. 1 shows, somewhat schematically, one embodiment of this invention.

FIG. 1A is a sectional view taken along 1A1A of FIG. 1.

FIG. 2 shows a modification of the invention shown in FIG. 1.

FIG. 3 shows another embodiment of the present invention.

FIG. 4 shows still another embodiment of the inventron.

In FIG. 1, numeral 1 denotes a metal enclosure which could be, for example, of round, rectangular, or elliptical cross-section. Within this enclosure are situated four coaxial cable terminals 2, 3, 4 and 5. The enclosure comprises a metal or other conductive housing defining a main cavity 1 from which parallel hollow arms 6 extend in pairs. Each pair of hollow arms 6 are quite closely adjacent each other and parallel and are joined at their outer ends by a hollow connecting member or leg '7. As shown there are four pairs of hollow arms 6 extending from the main cavity 1. The adjacent faces of each pair of legs 6 are slightly offset to define relatively close opposed faces constituting and defining gaps 9, 1t 11 and 12.

Within the main cavity 1 are four coaxial cable terminals 2, 3, 4 and 5. In the drawings these terminals are shown somewhat schematically but may be of conventional form comprising connecting means for coaxial cables wherein the outer conductor is electrically conected to the metal of the housing 1 and the inner conductor is insulated therefrom. A coaxial cable 13 is connected across each of the gaps 9, 10, 11 and 12 but having its outer conductor connected to the wall at one side of the gap and its inner conductor extending across the gap to the other wall. Each of the cables 13 extends along the interior of a leg 6 to a suitable coaxial cable terminal 14, 15, 16, or 17 preferably located within the connecting member 7. The combination of a gap 9, 1t), 11 or 12 and its corresponding coaxial line 13 form a balance to unbalance transformer, also known in the art as a balun gap structure.

Connecting between the terminals 2, 3, 4 and 5, and

the gaps 9, 10, 11 and 12 are four groups of coaxial transmission lines, 18, 19, 20 and 21. There are four transmission lines in each group and each transmission line in a group has the same electrical length and characteristic impedance as the other lines in the same group but not necessarily the same as the lines in other groups. The diiferent groups of transmission lines are connected across the gaps in different patterns. The patterns are related in that the transmission lines from any one group are connected across the gaps in the same direction as two of the transmission lines from any other group and in the opposite direction from the remaining two transmission lines. It is this method of connection which insures isolation of the input terminals 2, 3, 4 and 5. For example, if a signal is introduced into terminal 2, voltages will be caused to appear across the gaps 9, 10, 11 and 12 via transmission lines 18. This in turn will cause voltages to appear at ports 14, 15, 16 and 17. The voltages at terminals 14 and 15 are one hundred eighty degrees out of phase with the voltages appearing at terminals 16 and 17. The gap voltages will also cause currents to flow in the transmission lines 19 connecting to terminal 3. At gaps 9 and 11 the voltage introduced into the transmission lines 19 will be in phase with the voltages in the transmission lines 18. At gaps 10 and 12 the voltages introduced into the other transmission lines 19 will be one hundred eighty degrees out of phase with the voltages in the transmission lines 18. These four introduced voltages will add at terminal 3 to result in a voltage node at all frequencies provided that the transmission lines 18 are all of equal electrical length and impedance and that the transmission lines 19 are also all of equal electrical length and impedance although the two groups need not be equal to each other. In a similar manner a node is caused to appear at terminal 4 due to in-phase voltages appearing at gaps 9 and 10 and one hundred eighty degree out of phase voltages appearing at gaps 11 and 12. Likewise terminal 5 is isolated due to the resulting cancellation of in-phase voltages appearing at gaps 9 and 12 by one hundred eighty degree out of phase voltages from gaps 11) and 11.

If signals are introduced at the four terminals, 2, 3, 4 and 5,

the voltages appearing at the four terminals 14, 15, 16, 17 are Suitable corrections must be made for the phase lag caused by the electrical length of the transmission lines in the structure.

It should be recognized that the isolation of the input terminals from each other is not frequency sensitive and is determined only by the equality of lines electrical length and gap structure.

FIG. 2 shows a variation of the invention of FIG. 1 which is included in order to show an embodiment wherein the number of independent input terminals is less than the number of gaps. Numeral 22 represents the hollow enclosure, numerals 23, 24 and 25 represent three coaxial cable input terminals, numeral 26 denotes four pairs of hollow members extending from enclosure 22 and joined at their outer ends by cavities 2'7. Numerals 29, 30, 31 and 32 indicate gaps which may be considered identical to those of FIG. 1. The combination of the gaps 29, 3t 31 and 32, the hollow members 26, the cavities 2'7,

=3 the coaxial lines 33 and the terminals 34, 35, 36 and 37 form four balance to unbalance transformers. In this figure there are three groups of coaxial transmission lines 38, 39 and 44 Groups 38 and 39 have four transmission lines each while group 40 has two transmission lines. Isolation between terminals 23 and 24 is derived from cancellation of in-phase voltages at gaps 29 and 32 by one hundred eighty degree out of phase voltages at gaps 30 and 31. Isolation of terminal 25 is derived from cancellation of an in-phase voltage from gap 29 by a one hundred eighty degree out-of-phase voltage from gap 32. The voltages appearing at terminals 34, 35, 36 and 37 by voltages introduced at terminals 23, 24 and 25 are as follows:

34 "ias-l- 24 25 30 23 24 V36: 23 24 37 2s+ 24 25 Again suitable corrections are to be made for the phase lag caused by the electrical length of the transmission lines in the structure. It should be recognized that the number of independent input ports and the number of gaps within the structure can be varied so long as mutually cancelling voltages are obtained at the input ports.

FIG. 3 illustrates a further embodiment of this inven tion as applied to antennas, Numeral 41 represents a hollow metallic structure which is used both as a support structure and as a central cavity. Numeral 42 denotes the opposed hollow members extending laterally from the central cavity 41. Two hollow members 43 are at tached to the members 42 and are oriented parallel to the long axis of the central cavity 41. The ends of members 43 are turned toward the central cavity 41 but do not touch it. Other hollow members 45 extend from the central cavity 41 toward each of the hollow members 44. The spaces existing between adjacent hollow members 44 and 45 form gaps 46, 4-7, 48 and 4?. Within the central cavity 1 are three coaxial cable input terminals 50, 51 and 52, to each of which one of three groups 53, 54 and 55, of four coaxial transmission lines of equal electrical length are connected. These transmission lines pass inside the hollow members and connect to the gaps in the directions shown with only one coaxial line from each group connecting across any one gap. The connections across the gaps are arranged such that the terminals 50, 51 and 52 are isolated from one another in the manner fully described with relation to the previous embodiments. The connections are also so made as to cause the structure to act as an antenna capable of functioning in three independent modes. A voltage introduced into terminal 59 will cause the structure to radiate as a vertical loop antenna. Currents will be caused to flow in a counter-clockwise direction around the outside of the structure through members 43, 44 and 45 and transversely across the central cavity 411. No currents will flow in the center legs 42 and no currents will flow along the long axis of the central cavity 41 for this mode of operation. Since the terminals 50, 51 and 52 are isolated no voltages will appear at terminals 51 and 52.

A voltage introduced into terminal 51 will cause a current to flow to the left in the top of the structure which will be equal to a similar current also flowing to the left in the bottom of the structure. These currents will add and flow to the right on the members 42. The structure, for this mode of operation, then acts as a vertical array of two horizontally polarized folded dipoles having a common leg.

The introduction of a voltage into terminal 52 causes currents to flow in a downward direction on the members 42 and in an upward direction along the long axis of the central cavity 41. This causes the structure to act as a horizontal array of two vertically polarized folded dipoles having a common leg.

FIG. 4 shows a further embodiment of this invention as applied to a unidirectional coplanar spaced loop antenna of the type described in the patent to C. B. Watts, J r., Patent No. 2,972,145. In the patent device a unidirectional radiation pattern is obtained by the addition of the radiation patterns of an array of two loops excited in-phase with the radiation pattern of two loops fed at plus and minus ninety degrees respectively with respect to the in-phase loops. A resistor is used to obtain the quadrature phase relationship and to compensate for the relative efficiencies of the two modes.

In FIG. 4, numerals 56 and 57 represent two hollow loops of regular cross-section joined to opposite ends of a central cavity 58. Gaps 59 and 66 exist in the loops symmetrical with respect to the central cavity 58 and diametrically opposite to the points where the loops join the cavity. Within the cavity 58 and extending from it are two coaxial cable inputs 61 and 62. Connected to input 61 are two coaxial lines 63 and 64. Line 63 is connected across gap 60 and line 64 is connected across gap 59.

These connections are made such that the currents which are caused to flow on the loop members by a voltage introduced at input 61 cause the loops to radiate in aiding phase while a voltage introduced into the lines and 66 from input 62 causes the loops to radiate in phase opposition. Input terminals 61 and 62 are isolated from each other since a voltage introduced at 62 causes an in-phase voltage in line 63 to cancel a one hundred eighty degree out-of-phase voltage in line 64 at terminal 61.

Throughout the structures described herein all coaxial cable connections are made through terminals having the characteristics of the terminals 2, 3, 4 and 5 described with reference to FIG. 1 and all connections of those cables to the gaps, in each form of the invention, are made in the manner described with reference to the connection of cables 13 thereto. Reference herein is made to the direction of the connection across a gap, By this terminology applicant intends to indicate the particular side of the gap to which the outer conductor is connected with reference to the side of the gap to which the inner conductor is connected. For example, any two cables having their outer conductors connected to the same side of the gap and their inner conductors connected to the opposite wall are said to be connected to said gap in the same direction. On the other hand, any pair of cables connected to the same gap with their outer conductors connected to opposite walls and their inner conductors connected to opposite walls are said to be connected to the gap in opposite directions.

While four specific embodiments and variations of the invention have been described and shown in detail, it is to be understood that other forms may be resorted to within the scope of the appended claims.

I claim:

1. A multiple-mode structure comprising: a metal enclosure having a plurality of coaxial cable input terminals in a wall thereof; an even number of symmetrical pairs of hollow extensions on said enclosure, each pair having opposed spaced wall portions defining a balun gap structure; a plurality of coaxial transmission lines leading from each of said input terminals to said gap structures and being connected thereacross, all the transmission lines from any one input terminal being of the same electrical length; said coaxial transmission lines being connected across said gaps, with transmission lines from any one input terminal being connected across certain of said gaps in the same direction as the corresponding lines from another input terminal and across an equal number of gaps in the opposite direction as lines from that same other terminal, whereby all currents from any one input terminal that appear at any other input terminal appear thereat in bucking relation so as to cancel out, whereby said input terminals are effectively isolated from each other.

2. A structure as defined in claim 1 wherein said coaxial transmission lines extend from said input terminals to said balun gaps within said enclosure.

3. A structure as defined in claim 1 including a coaxial output cable connected across each of said gaps.

4. A structure as defined in claim 1 wherein there are the same number of said input terminals as there are gaps; there being a transmission line from each terminal to each gap.

5. A structure as defined in claim 1 wherein the number of said gaps exceeds the number of said input terminals; there being a transmission line from at least one of said terminals to each gap and a transmission line from certain other terminals to less than all of said gaps.

6. A structure as defined in claim 1 wherein at least certain of said hollow extensions are arranged to define, with said enclosure, a radiating loop antenna interrupted by certain of said gaps; one of said input terminals having a transmission line connected to said certain of said gaps in said loop in the same direction around said loop.

7. A structure as defined in claim 6 wherein said enclosure is of elongated form; certain of said extensions extending laterally therefrom in opposed relation and being formed at their outer ends to extend in opposite directions parallel to said enclosure then inwardly toward others of said extensions on said enclosure to define said gaps.

8. A structure as defined in claim 7 wherein said enclosure and extensions are arranged to define an elongated central cavity with a hollow loop at each end thereof; there being one of said gaps in each of said loops.

References Cited by the Examiner UNITED STATES PATENTS 2,341,408 2/ 1944 Lindenbald 333-9 2,511,899 6/1950 Brown 333-9 2,724,806 11/ 1955 Tillotson 33326 2,976,497 3/1961 Watts 33311 HERMAN KARL SAALBACH, Primary Examiner. 

1. A MULTIPLE-MODE STRUCTURE COMPRISING: A METAL ENCLOSURE HAVING A PLURALITY OF COAXIAL CABLE INPUT TERMINALS IN A WALL THEREOF; AN EVEN NUMBER OF SYMMETRICAL PAIRS OF HOLLOW EXTENSIONS ON SAID ENCLOSURE, EACH PAIR HAVING OPPOSED SPACED WALL PORTIONS DEFINING A BALUN GAP STRUCTURE; A PLURALITY OF COAXIAL TRANSMISSION LINES LEADING AND BEING OF SAID INPUT TERMINALS TO SAID GAP STRUCTURES AND BEING CONNECTED THEREACROSS, ALL THE TRANSMISSION LINES FROM ANY ONE INPUT TERMINAL BEING OF THE SAME ELECTRICAL LENGTH; SAID COAXIAL TRANSMISSION LINES BEING CONNECTED ACROSS SAID GAPS, WITH TRANSMISSION LINES FROM ANY ONE INPUT TERMINAL BEING CONNECTED ACROSS CERTAIN OF SAID GAPS IN THE SAME DIRECTION AS THE CORRESPONDING LINES FROM ANOTHER INPUT TERMINAL AND ACROSS AND EQUAL NUMBER OF GAPS IN THE OPPOSITE DIRECTION AS LINES FROM THAT SAME OTHER TERMINAL, WHEREBY ALL CURRENTS FROM ANY ONE INPUT TERMINAL THAT APPEAR AT ANY OTHER INPUT TERMINAL APPEAR THEREAT IN BUCKING RELATION SO AS TO CANCEL OUT, WHEREBY SAID INPUT TERMINALS ARE EFFECTIVELY ISOLATED FROM EACH OTHER. 